Currently, Scala's HasSeed mix-in uses a random Long as the default value for seed. Python uses 42. After discussions, we've decided to use a seed which varies based on the class name, but which is fixed instead of random. This will make behavior reproducible, rather than random, by default. Users will still be able to change the random seed.
The default seed should be produced via some hash of the class name.
Scala's seed will be fixed in a separate patch.